Fail fast on directory already exists

[ssteinerx]

• Cookiecutter version: 1.4.0
• Template project url: local
• Python version: 2.7
• Operating System: 10.10.6

Description:

If the destination directory already exists (based on the project name), cookiecutter fails after all questions are asked.

What I've run:

cookiecutter, fill out name of existing directory should fail as soon as it can detect, not after answering all of the questions.

[hackebrot]

I see how checking the target directory while prompting would improve the user experience.

Do you want to create a PR, @ssteinerx?

[ssteinerx]

Unfortunately, prompt.prompt_for_config doesn't know anything about what is being asked; it just iterates through the given context and collects the specified information.

The 'context' is just the parsed cookiecutter.json, so there's no information there vis-à-vis validation of inputs. The json just holds the prompts and default values.

Special-casing this one thing by name could be done but ick.

Without major rearrangement of cookiecutter.json to have validation hooks etc. (and essentially rewriting all the associated routines), or gluing on some special-case side-car validation gizmo onto prompt_for_config, there's no obvious/non-icky way of handling this with the current architecture.

[hackebrot]

Thanks for investigating, @ssteinerx! 🙇

Sounds like another feature for #848 to me.

[ssteinerx]

@hackebrot Yes, I didn't have time to read the spec, but this type of fail-fast should be built in somehow.

[theodesp]

I see that we can decorate the prompt_for_config with something like a context aware prompt that will trigger extra actions when detecting special keys.

For example if it detects a key named project_slug will trigger a callback to check if the folder exists.

I think it's possible to do with out breaking changes. That will be a chance to refactor the prompt.py

[ssteinerx]

@theodesp I haven't looked at this in quite a while (like 8 months!), but I remember thinking that I'd want to have a way of indicating that prompt invokes action-type validator action-type-validator e.g.:

I haven't got time to look right this second, but I vaguely remember wanting something like:

prompt("Create the docs directory?", action_type="create-directory", validator="prompt-overwrite-if-exists-or-exit")

[theodesp]

Yes thats another good idea. As you said prompt.prompt_for_config doesn't know anything about what is being asked: So we need to keep the existing functionality. Maybe if we pass a map of keys to validators as a parameter that will get called if the particular key was prompted and filled as I dont see any support for validation in click prompt http://click.pocoo.org/5/api/#click.prompt